Preparation of electrolyte



Jan. 17, 1956 T. R. YOUNG ETAL PREPARATION OF ELECTROLYTE Filed Jan. 21. 1953 PREPARATIUN F ELECTROLYTE Thomas R. Young, Riverside, Conn., and Robert L.

Somerville, Neshanic, N. J., assignors, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey Application January 21, 1953, Serial No. 332,328

2 Claims. (Cl. 204-6/1) This invention relates to the electrolytic production of metallic titanium and metallic zirconium and, more particularly, to a cyclic method wherein spent electrolyte from the titanium or zirconium production stage may be completely recovered and re-used in the electrolytc operation. t

The production of metallic titanium and metallic zirconium by electrolytic deposition from a fused salt bath containing an alkali metal-titanium or zirconium double iiuoride (an alkali metal fluotitanate or iluozirconate) has been developed to the stage where the metal so `produced is of high purity. From a commercial standpoint, however, the cost of producing metal by this procedure is a serious draw-back due largely to the cost of raw materials including the fluorine component of the double iluoride. We have now discovered that the cost of raw materials for such a process of electrolytically producing metallic titanium and metallic zirconium can be markedly reduced by appropriate choice of the diluent salt bath and by appropriate conversion of the by-products of the electrolysis. Thus we have found that the completely cyclic handling of all by-products of the electrolysis may be achieved without the build up of any one or more of the elements of the electrolytic bath.

The success of our recyclic operation in the elcctrolytic production of metallic titanium or metallic zirconium from a fused salt bath is dependent upon the use as the immediate source of the titanium or zirconium of a compound oi such metal the anion of which is restricted to one or more of the elements chlorine, oxygen and carbon, by the use as another component of the salt bath of one or more alkali metal chlorides, and advantageously by the use or by-product chlorine from the electrolytic cell as the chiorinating agent for the transformation of the titaniierous or zirconiferous source material into a titanium or zirconium chloride which cansubsequently be readily converted to the corresponding alkali metal double iluoride, Thus, our invention comprises an improvement in the production oi metallic titanium or metallic zirconium wherein a double fluoride of titanium or zirconium and an alkali metal is electrolyzed in a fused salt bath comprising this double fluoride dissolved or otherwise contained in an alkali metal chloride, the products of the electrolysis comprising deposited metallic titanium or zirconium, evolved chlorine gas and an alkali metal fluoride-containing spent electrolyte. Our improvement in such a process comprises reacting the spent electrolyte from the aforesaid nite States Patent O electrolysis with a titanium or zirconium chloride with the resulting formation of an alkali metal-titanium or zirice The titaniferous sources useful in practicing our invention include oxidic compounds such as titanium dioxide, native rutile, titanium carbonate, titanium cyano-nitride (TiCaNt/Oa) and titanium slag concentrates such as those produced as described in the United States patent to Peirce et al. No. 2,476,453. Each or" these source materials is readily available and is relatively free of such contaminants as would build up extraneous impurities in the process. When titanium dioxide is used as the starting material, We have found it advantageous to use anatase titanium dioxide pigment, but other forms of the dioxide may be used with advantage. The zirconiferous materials useful in practicing our invention include similar oxidic zirconiferous materials such as zirconium oxides, zir* conium carbonate and zirconium slag concentrates. Thus, inasmuch as the raw materials as well as the chemistry of our process are substantially the same for zirconium as for titanium, We shall coniine our subsequent description of the invention to the production of metallic titanium with the understanding, of course, that what is said in this regard applies with equal force to the corresponding production of metallic zirconium.

The only other raw material required in significant amounts for the practice of our invention is therefore the carbonaceous reducing agent, and although carbon is preferably used for this purpose the carbonaceous reducing agent may be supplied in the form of carbon monoxide or a hydrocarbon. Each of these carbonaceous materials is capable of promoting the conversion of oxidic titauiterous and zirconiferous materials to the corresponding chlorides in the presence of elemental chlorine. By control oi reaction conditions and proportions of the reactants, either the tetrachlorides or lower chlorides such as diand trichiorides may be produced, and each of these tetravalent and lower valence titanium and zirconium chlorides may be used in producing the corresponding double fluorides which, in turn, may be used in the electrolytic cell pursuant to our operation.

The process of our invention will be readily understood by reference to the accompanying low sheet. As shown therein, an alkali metal-titanium double lluoride, such as potassium titanium fluoride (also known as potassium l'luotitanate, KzTlFs) and at least one alkali metal chloride such as sodium chloride are charged to an electrolytic cell l as the essential components of the electrolytic bath. The cell is heated to maintain these salts in fused condition in the cell. Electrolysis of the resulting bath, which may contain, for example, 2 to 30% by weight of the double liuoride, results in the deposition at the cell cathode of metallic titanium which may be removed in any appropriate manner. Chlorine gas is evolved at the anode and is delivered from the cell to the chlorinator 2t. The titaniferous source material such as titanium dioxide is charged to the chlorinator along with carbon and heat is supplied in order to promote reaction oi these charge components with the resulting evolution of titanium tetrachloride vapor. The titanium tetrachloride, either in its gaseous or liquid form, is then delivered to the reactor 3 either directly or with intervening purilication if desirable. Spent electrolyte is withdrawn from the cell l either intermittently or continuously, and is also delivered to the reactor 3. rl`his spent electrolyte, which contains an alkali metal iluoride as its essential component, may be either cooled and then charged directly to the reactor 3 or it may he broken up into a slurry with extraneous water or other suitable wash liquor from another stage of the process and be delivered in this form to the reactor 3. Small amounts of an alkali metal chloride such as potassium chloride and a source of iiuorine such as hydroiluoric acid may also be added to the reactor 3 in order to make up for any mechanical loss of the alkali metal-chlorineand ilumine-.components of 3 the fused salt bath and thus insure the presence in the reactor of substantially stoichiometric quantities of all essential reagents for the formation of an alkali metal-titanium double uoride.

inasmuch as the electrolysisof the fused s alt bath is preferably carried out under an inert atmosphere, advantageously of a monatomic gas such as argon, the argon will be discharged from the cell along with the chlorine. However, the argon will pass through the chlorinator 2 and can thus be returned to the cell 1 preferably with intervening treatment in a purifier i to remove any extraneous gas such as nitrogen from leakage or carbon dioxide from the burning of propane, or to remove a gaseous impurity introduced into the system along with the argon.

The reaction between the titanium tetrachloride and the recirculated spent electrolyte, inthe presence of water advantageously supplied as the aqueous medium of the spent electrolyte slurry charged to the reactor 3, together with addedmake-up reagents, takes place in the reactor upon heating this mixture to a temperature close to the boiling point of water at atmospheric pressure, i. e., to up to about 100 C. by means of steam coils or the like. The resulting alkali metal-titanium double fluoride solution, such as a potassium-titanium uoride solution, is Withdrawn from Vthe reactor and is concentrated to crystallize out of the solution both the double fluoride and a portion of the contained alkali metal chloride. We have found that this result can be obtained particularly satisfactorily in a triple effect evaporator, but regardless of the method of separating the double iiuoride and the alkali metal chloride these separated salts are passed through driers 5 and 6 and thence back to the electrolytic cell 1. It will be seen, accordingly, that the only extraneous source materials for this continuous production of titanium metal comprises the 1 titaniferous source material, such as titanium dioxide, and

carbon for the generation of titanium chloride from the chlorine effluent from the cell.

As pointed out hereinbefore, we have found that a triple effect evaporator may be used with particular advantage in the recovery` of the solid alkali metal-titanium double fluoride and alkali metal chloride from the solution thereof withdrawn from the reactor 3. In the operation of the triple effect evaporator in accordance with our invention, the alkali metal-titanium double liuoride and alkali metal chloride solution (such, for example, as an aqueous solution of potassium titanium uoride and sodium chloride) is delivered to the third effect of the evaporator. The solution is concentrated in the third effect by the combination 'of a reduction in pressure, such as operation under a vacuum of say 27 inches of mercury, and by the heat supplied by steam which has previously been used as the heating medium for the first two effects. The liquor in the third effect is thus concentrated at a temperature of about 50 C. with the result that potassium titanium fluoride Y The resulting slurry of the y crystals form in the liquor. double fluoride is discharged from the third effect to a separator 7, and the separated double fluoride is delivered to the drier 5. A portion of the mother liquor removed from the double liuoride in the separator 7 may be returned to the reactor 3 and the remainder of the liquor is delivered to the Vsecond eect of the evaporator. Inasmuch as the second effect operates at a higher temperature, generally about 90 C., the further evaporation of water from the liquor introduced into the second effect from the separator 7 results in crystallization of sodium chloride. The resulting slurry is discharged from the second effect to a separator 8 from which the separated sodium chloride is de-V livered to the drier d. A portion of the liquor separated from the sodium chloride in the separator 8 is advantageously returned to the third effect and the remainder of this liquor is delivered to the first effect of the evaporator. inasmuch as the heating steam for Vthe evaporator passes through the first effect before the second and third effects, the .temperature of the liquor in the first effect is raised to a1 still higher temperature, about 130 C. Although a trolyte.

Aconsiderable amount of water is evaporated from the liquor in the first effect, with the resulting crystallization of some sodium chloride, the resulting slurry is delivered to the second effect Where further evaporation, though at a lower prevailing operating temperature, effects more complete crystallization of sodium chloride which is then recovered in the separator 8.V On the other hand, the potassium titanium uoride contained in the aqueous phase in both of these relatively high temperature effects will remain in solution and will not crystallize from the solution to any significant extent until it is delivered to the third effect which, as noted hereinbefore, advantageously operates at a relatively low temperature Vof about 50 C.

The process of our invention may be Villustrated by, but is not limited to, the following specific example thereof:

A fused salt bath composed of potassium iluotitanate and sodium chloride in which the potassium fluotitanate formed 25% Vof the initial weight of the bath, was electrolyzed in an electrolytic cell maintained under an inert atmosphere of argon gas. For each mol of potassium fiuotitanatethatwas decomposed at the cathode, one mol of titanium was deposited on the cathode, two mols of potassium tiuoride were formed, four mols of sodium chloride were converted'to four mols of sodium fluoride, and two rnols of chlorine gas were evolved from the elec- Chlorine gas evolved from the fused salt bath at the anode and titanium metal was deposited on the cell cathode. Spent electrolyte depleted in potassium liuotitanate and sodium chloride content, and containing potassium fluoride and sodium fluoride in anlramount stoichiometrically equivalent to the amount of potassium fluotitanate electrolytically decomposed bythe electrolysis, was withdrawn from the electrolytic cell in the vicinity of the cathode.

The chlorine gas evolved from the electrolytic cellwas introduced into a chlorinator in which it chlorinated a heated mixture of titanium dioxide and carbon to form titanium tetrachloride. VThe spent electrolyte containing potassium fluoride and sodium fluoride as its essential components' was cooled to ambient temperature and the cooled spent electrolyte was charged with extraneous water into a reactor maintained at about the boiling point of water by means of steam coils. The titanium tetrachloride from the chlorinator was then introduced into the reactor where it reacted in an aqueous medium with the spent electrolyte.

The spent electrolyte and titanium tetrachloride reacted together in the hot aqueous medium to form soluble reaction products. The aqueous solution from the reaction vessel was then introduced into the third effect of a triple effect evaporator, thetemperature of the liquor of which was maintained at about 50 C. Vapor evaporated from the liquor in the third effect was withdrawn therefrom by a conventional condenser and vacuum pump arrangement. Concentrated liquor from the third, effect was introducedk into a separator from which potassium fluotitanate crystallized from the solution was withdrawn. The crystallized potassium fluotitanate was then dried preparatory to introducing this material into the fused salt electrolyte contained in the electrolytic cell.

Concentrated liquor from the separator of the third effect was introduced into the second effect in which the liquor was maintained at a temperature of about 90 C. Vapor evaporated from the liquor in the second effect was introduced into the steam chest vof `the third effect as in conventional practice. `The concentrated liquor from the second effect containing crystals of sodium chloride was introduced into a separator from .whence the crystallized liquor therein. Concentrated liquor from the first effect was introduced into the second eifect for further concentration of its salt content.

The potassium lluotitanate obtained from the dryer associated with the separator of the third efect and the sodium chloride obtained from the dryer associated with the separator of the second effect were introduced into the fused salt electrolyte being electrolyzed in the electrolytic cell. The amount of titanium (in the form of titanium dioxide) which reacted with the chlorine gas evolved from the electrolytic cell, and the amount of the resulting titanium tetrachloride which reacted with the potassium fluoride and sodium fluoride content of the spent electrolyte, was stoichiometrically equivalent to the amount of potassium iluotitanate electrolytically decomposed by the cell to form titanium metal, chlorine gas and said spent electrolyte.

Typical spent electrolytes resulting from the electrolysis of an alkali metal lluozirconate-alkali metal chloride bath are set forth in a copending application Ser. No. 279,471, now Patent 2,687,340. Expressed as ions three such baths are disclosed as follows:

Each of these spent electrolytes may be readily regenerated in accordance with our invention by reacting the spent electrolyte with the zirconium tetrachloride, obtained by chlorinating a suitable zirconium containing material with the chlorine obtained during the electrolysis producing the spent bath, in a manner well known in the art, e. g., by bringing the chlorine and zirconium compound together at an elevated temperature in the presence of carbon. The amount of zirconium tetrachloride employed should be that necessary to provide a stoichiometric quantity to produce the desired double fluoride when combined with the fluorine content of the spent electrolyte.

It will be seen, accordingly, that the process of our invention makes possible the continuous production of titanium or zirconium metal by electrolysis'of a fused salt bath comprising an alkali metal-titanium or zirconium double fluoride and an alkali metal chloride and that our process makes it possible to regenerate these bath components from the spent electrolyte without the introduction into the process, either as the titaniferous or zirconiferous source material or as the digesting medium for these materials, of any elements which would tend to accumulate in the cyclic operation which characterizes our process. The only extraneous elements introduced into our process are limited to oxygen, carbon and hydrogen, and each of these elements ultimately is consumed in the formation of water or a permanent gas which is readily discharged from the process as outlined hereinbefore. The relatively expensive components ofthe system, particularly the fluorine and alkali metal components, are thus continuously recycled. The commercial appeal of the electrolytic production of titanium and zir- `conium metal is thereby enhanced and an integrated process is obtained in which only relatively simple forms of raw materials are required for the continuous production of these metals in a state of high purity.

We claim:

1. In the production of a metal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of an alkali metal chloride and a double fluoride of an alkali metal and a metal of the group consisting of titanium and zirconium is electrolytically decomposed with, (l) the resulting production of an electrodeposit of said metal on a cathode, (2) the evolution of chlorine gas at an anode, and (3) the formation of a spent electrolyte consisting essentially of at least one alkali metal fluoride; the improved method of regenerating material suitable for reuse as the fused salt bath in the aforesaid electrolytic process from said evolved chlorine and said spent electrolyte as follows: reacting the evolved chlorine with carbon and an oxidic compound of said metal to produce a tetrachloride of said metal; heating to up to about C. an aqueous solution of the spent electrolyte and said tetrachloride in which the relative amounts of the alkali metal, halogen and metal of the group consisting of titanium and zir coniurn present are substantially the stoichiometric proportions necessary for the formation of a double fluoride of an alkali metal and of said metal and an alkali metal chloride thereby producing an aqueous solution of a double fluoride of said metal and an alkali metal and an alkali metal chloride, and recovering said products for reuse in a repetition of the electrolytic process.

2. In the production of a metal of the group consisting of titanium and zirconium wherein a fused salt bath consisting essentially of an alkali metal chloride and a double fluoride or" an alkali metal and a metal of the group consisting of titanium and zirconium is electrolytically decomposed with, (l) the resulting production of an electrodeposit of said metal on a cathode, (2) the evolution of chlorine gas at an anode, and (3) the formation of a spent electrolyte consisting essentially of at least one alkali metal fluoride; the improved method of regenerating material suitable for reuse as the fused salt bath in the aforesaid electrolytic process from said evolved chlorine and said spent electrolyte as follows: reacting the evolved chlorine with carbon and an oxidic compound of said metal to produce a tetrachloride of said metal; and heating to up to about 100 C. an aqueous solution of the spent electrolyte and saidtetrachloride in which the relative amounts of alkali metal, halogen and metal of the group consisting of titanium and zirconium present are substantially the stoichiometric proportions necessary for the formation of a double fluoride of an alkali metal and of said metal and an alkali metal chloride thereby producing an aqueous solution of a double fluoride of said metal and an alkali metal and an alkali metal chloride, charging the aqueous medium to the third effect of a triple elect evaporator and therein concentrating the aqueous medium to an extent sufficient to promote crystallization therefrom of the double fluoride, crystallizing the double fluoride, recovering the crystallized double fluoride from the ellluent from the third eilect of the evaporator, delivering the remaining aqueous medium to the second and first effects of the evaporator, further concentrating the aqueous medium therein to an extent suicient to promote crystallization of the alkali metal chloride, crystallizing the alkali metal chloride, recovering the crystallized alkali metal chloride, and returning said crystallized double fluoride and said crystallized chloride to the salt bath for the preparation of additional metal.

References Cited in the Ille of this patent UNITED STATES PATENTS 1,801,661 Collngs Apr. 21, 1931 2,687,340 Wainer Aug. 24, 1954 FOREIGN PATENTS 574,832 Great Britain l an. 22, 1946 OTHER REFERENCES Worner et al.: The Extraction of Titanium, Proceedings of the Australasian Institute of Mining and Metallurgy, New Series, No. 158-9, 1950, page 80.

Journal of Applied Chemistry (U. S. S. R.), vol. 13, 1940, pages 51 thru 55; paper by Sklarenko et al.

Treatise on Chemistry, by Roscoe et al., vol. 2 (1913), page 815. 

1. IN THE PRODUCTION OF A METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WHEREIN A FUSED SALT BATH CONSISTING ESSENTIALLY OF AN ALKALI METAL CHLORIDE AND A DOUBLE FLUORIDE OF AN ALKALI METAL AND A METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM IS ELECTROLYTICALLY DECOMPOSED WITH, (1) THE RESULTING PRODUCTION OF AN ELECTRODEPOSIT OF SAID METAL ON A CATHODE, (2) THE EVOLUTION OF CHLORINE GAS AT AN ANODE, AND (3) THE FORMATION OF A SPENT ELECTROLYTE CONSISTING ESSENTIALLY OF AT LEAST ONE ALKALI METAL FLUORIDE; THE IMPROVED METHOD OF REGENERATING MATERIAL SUITABLE FOR REUSE AS THE FUSED SALT BATH IN THE AFORESAID ELECTROLYTIC PROCESS FROM SAID EVOLVED CHLORINE AND SAID SPENT ELECTROLYTE AS FOLLOWS: REACTING THE EVOLVED CHLORINE WITH CARBON AND AN OXIDIC COMPOUND OF SAID METAL TO PRODUCE A TETRACHLORIDE OF SAID METAL; HEATING TO UP TO ABOUT 100* C. AN AQUEOUS SOLUTION OF THE SPENT ELECTOLYTE AND SAID TETRACHLORIDE IN WHICH THE RELATIVE AMOUNTS OF THE ALKALI METAL, HALOGEN AND METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM PRESENT ARE SUBSTANTIALLY THE STOCIHIOMETRIC PROPORTIONS NECESSARY FOR THE FORMATION OF A DOUBLE FLUORIDE OF AN ALKALI METAL AND OF SAID METAL AND AN ALKALI METAL CHLORIDE THEREBY PRODUCING AN AQUEOUS SOLUTION OF A DOUBLE FLUORIDE OF SAID METAL AND AN ALKALI METAL AND AN ALKALI METAL CHLORIDE, AND RECOVERING SAID PRODUCTS FOR REUSE IN A REPETITION OF THE ELECTROLYTIC PROCESS. 